When bones increase in thickness (diameter) as an individual grows to adulthood, which tissue or cells of the bone begin this growth process?

A. Cells of the periosteum differentiating into osteoblasts
B. Chondrocytes at the epiphyseal plate migrating to the bone's surface
C. Osteocytes near the bone's surface reverting to osteoblasts
D. Endosteal cells migrate to the periosteum and calcify
E. Collagen fibers in the periosteum form a new layer on the bone surface and become calcified

Osteoblasts are the bone cells responsible for bone formation and play a key role in increasing bone thickness (diameter) as an individual grows to adulthood. Osteoblasts synthesize and secrete the extracellular matrix of bone tissue, including collagen fibers, which contribute to the growth process.

Adjacent to the bone's surface, osteoblasts differentiate from osteoprogenitor cells, which are stem cells that give rise to osteoblasts. These osteoblasts deposit new bone matrix, contributing to the thickening of the bone.

Overall, the process of bone growth involves the concerted actions of various bone cells, with osteoblasts being particularly crucial in initiating and promoting the growth of bone tissue throughout development.

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